Recirculating pneumatic separator

ABSTRACT

A pneumatic separator for separating lighter particles from heavier stem particles and the like, as in tobacco threshing, including a separating chamber having air circulating in a generally upward path therethrough, an inlet rotary impeller mounted on one side of the separating chamber for thrusting particles to be separated into and across the chamber toward a generally upwardly extending opposite wall of the chamber, an inclined perforated plate member below the level of the impeller for directing larger particles discharged toward or falling onto the inclined plate member for collecting and carrying heavier particles from the chamber, and an air jet impeller located immediately above the inclined plate to discharge an air jet therefrom for directing material into a high arc trajectory into the chamber. An air diffusion granting assembly below the inclined perforated plate member receives air discharged from a fan and has a plurality of directional vanes for reducing air flow and velocity in selected portions of the separating chamber. Air discharge openings are located at a vertical position above the level of the impeller to provide air flow therethrough into the chamber in zones located above the height of such openings.

BACKGROUND AND OBJECTS OF THE INVENTION

The present invention relates in general to pneumatic separators forseparating heavier material from lighter material, such as, for example,the stems from fragments of tobacco leaves, and more particularly to arecirculating pneumatic separator for tobacco stemmery operations forseparating tobacco leaf fragments from stems of tobacco leaves.

Functions normally performed in a tobacco stemmery operation where wholeleaf tobacco is processed after leaving the auction warehouse floor areordering and conditioning of the tobacco leaves, threshing or removal ofthe lamina from the stem, separation of the lamina and stems, drying,and packing. The present invention is concerned with machinery forordering and conditioning the tobacco leaves, threshing or removal ofthe lamina from the stems, and separation of the lamina and stems. Thedrying and packing of the tobacco leaf fragments is then accomplished byother machinery.

Ordering and conditioning is normally accomplished by tumbling thetobacco in a rotating cylinder with a slightly declining axis ofrotation while spraying the tobacco with steam and water. The object ismoisten the tobacco making it more pliable and to raise its temperaturefor the same reason.

Threshing is accomplished by a rotating cylinder with pieces of flatsteel (teeth) projecting from the cylinder surface. The axis of rotationis horizontal with the tobacco evenly fed across the upper surface ofthe cylinder. The teeth grab the leaves, cutting some and tending totear the lamina from the stems. At the same time the tobacco is thrownradially outward by centrifugal force where it contacts a close fittingconcave or basket which encloses the lower portion of the rotatingcylinder. The concave has openings through which the tobacco may pass.In the early stages of threshing these openings are fairly large. Astandard basket may be a sheet of 1/4 inch plate rolled to just clearthe teeth. This rolled shape is then cut by torch into a series ofdiamond shapes with a 21/2 inch slot between each row of diamonds. Theslots run in the direction of rotation and the diamonds overlap. As thetobacco passes through there is additional cutting of stems and removalof lamina.

Threshing is not 100 percent efficient so several threshers are usedwith a separator or separators in between. Latter threshers have smalleropenings in the concaves and the last one may have 11/2 inch to 2 inchround holes.

After separation the lamina and stems are separately dried down to 10-11percent moisture, cooled and packed into containers by large hydraulicpresses for storage for a year or more. During storage, some of thenatural starches convert to sugars by natural fermentation.

The machine of the present invention is similar to the prior artrecirculating pneumatic separator described in Rowell U.S. Pat. No.3,608,716, which is designed to receive tobacco from the thresher in aneven flow into a regulated uprising air column such that the lighterfree lamina rises upward with the air stream and the heavier stem orstem with lamina attached, frequently referred to as flags, falldownward against the air flow to be ejected to the next thresher oranother separator. In the machinery of the type disclosed in the priorU.S. Pat. No. 3,608,716, a mixture of free lamina, attached lamina andstem, and clean stem is pneumatically conveyed from the thresher orprevious separator into the screening separator. Here the air passesthrough a rotating screen of perforated metal and is returned to thefan. The tobacco mixture falls down the back wall into a four bladedrotating air lock which passes the tobacco out of the air stream.

Immediately it falls into a high speed six bladed rotating inlet rotor.These blades with resilient tips impart a uniform velocity to thetobacco and hurl it into a chamber, shown at 7 in the patent. Areasonably even air flow uprising through the chamber is induced by afan or fans.

The lighter lamina or strip, as it is commonly called, has lesserinertia and is effected by the air stream immediately and starts on itsjourney upward. Stems and flag are less effected by the air since theyare heavier and continue more or less to the wall opposite the inlet. Anadjustable damper called a ski-jump is located at the lower end of thiswall, blocking air flow next to the wall to create a dead air space.

Without air flow, the stem and flag fall to the ski-jump and due to itsangularity are directed in the opposite direction and slightly downwardacross the air stream for the second pass. Some free lamina may bejarred loose and be re-entrained in the air stream.

The lighter material enters the strip discharge section and is lockedout to an inspection belt. Air exits each end of the screen, passesthrough dampers and enters the suction of one or the other of twointernal fans.

The internal fans blow into the bottom of the separating section,through a louvered screen to even the air flow and then upward through aperforated belt. The belt serves as an additional air flow equalizer andprevents the heavy material from falling into the bottom of theseparator.

The reason for a belt is to provide a means of keeping the perforatedholes from stopping up due to small material that may pass through theinternal screen seals and be held on the underside of the perforatedsurface. Using a perforated belt insures that the under surface isalways changing to become an upper surface allowing any material to beblown free.

Having completed the second pass across the air stream the heavymaterial slides across the perforated belt into a pneumatic pick-up tobe conveyed to the next thresher or the next separator.

In order to keep the system negative in regards to air pressure, air isbled from the discharge of the fans which convey between the machines(transport fans). All leakage is now on an inward direction which helpsto contain the dust and dirt. The make up air enters the machine throughholes along each side at the belt level helping to keep the belt sealsclean plus air is admitted at the upper end of the belt and blows alongthe belt surface to assist the heavy material out of the machine.

Air is also exhausted from between the belt from a trough located underthe upper surface of the belt. The trough creates a dead air space whichallows sand or other material to fall from the belt surface.

Too high air velocity in the separating chamber will cause stems andflags to go with the good strip. Too much stem is not desired and largepieces (called objectionable) are just that. Too low a separatingvelocity lowers the stem content of the separated strip but allows toomuch good threshed material to pass on to the next thresher orseparator. This results in further degradation of the strip and is to beavoided.

Separating air flow is grossly regulated by slide or louver dampers atthe suction side of the fans and is finely tuned by use of a singlebladed by-pass damper.

Separated strip after leaving the air stream passes through thedischarge lock and falls to a belt for delivery to an inspection andcollecting belt.

While the philosophy in the tobacco threshing and separating communityuntil a few years ago was to thresh increasing quantities of tobacco andproduce a more uniform product (:.e. strip) with less fines and, becauseof the higher loads, less larger particles, the present approach istoward more larger pieces which means once a particle is threshed fromthe stem, it should be separated at once without being subjected toadditional threshing or handling resulting in degradation of size.

While the recirculating pneumatic separator of the above identifiedpatent met the former requirements, the air jet impeller and airdiffusion grating features do not produce the results now desired. It isnow recognized that use of a high velocity air stream, while separatingmore of the good material, has the drawback of also carrying along stem,flag and unthreshed leaves leading to an unacceptable high stem content.However, if a high velocity air stream is used to separate, and then theair is slowed to drop stem, a high separating efficiency and low stemcontent can be achieved. By use of a novel air jet nozzle arrangement,the apparatus of the present invention is now able to direct thematerial coming off the air jet impeller vane into a high arctrajectory, so that the jet acts to break tangles or dislodge particles,and the high arc trajectory allows more time for the separating air tointeract so that, as the heavier material takes a more downward courseat the end of its trajectory, it falls into the area of highestvelocity. Because the tobacco is moving downward against the upward airflow, the relative air velocity is increased without an increase in airflow further enhancing the separation. Also, it has been recognized thattobacco, as it enters the threshing separating portion of itsprocessing, contains a very high proportion of sand or silica stuck toor embedded in the tobacco. Threshing and separating tend to dislodgethis very abrasive medium and it is desirable to remove it. Theapparatus of the present invention includes, as part of the air circuit,a large plenum or settling chamber designed to allow this sand to settleout of the air stream prior to entering the fans. This makes it possibleto use lighter construction fan wheels of higher efficiency withconsiderable savings to the user in power cost.

Other objects, advantages and capabilities of the present invention willbecome apparent from the following detailed description, taken inconjunction with the accompanying drawings illustrating a preferredembodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a vertical longitudinal section view through the recirculatingpneumatic separator;

FIG. 2 is a rear end elevational view thereof;

FIG. 3 is a detailed side elevational view of the air jet impeller,viewed from the end of the air jet impeller assembly nearest the viewer;and

FIG. 4 is a fragmentary side elevational view of the far end of theseparator.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawings, wherein like reference characters designatecorresponding parts throughout the several figures, the recirculatingpneumatic separator of the present invention is housed within the casingstructure 11 and the material to be segregated by the pneumaticseparator, for example whole leaf tobacco, is fed into the casingstructure 11 through an inlet 12, shown in FIG. 1. A rotary screen 13 isprovided with a mesh of sufficiently fine size so that it prevents thematerial being brought into the separator from passing therethrough,although the conveying air which brings the material into the separatorpasses through the screen and out through an open end 14. Thus theconveying air for the material being fed into the separator forms aclosed circuit, passing into the separator through the inlet 12 and outthrough the passageway 14. There is provided an air lock 15 comprising aplurality of rotary gates which permit the material to be segregated topass therethrough but prevents any substantial quantity of the conveyingair from passing through into the main portion of the pneumaticseparator. The material to be treated within the separator passesdownwardly where it is engaged by a rotary impeller 16 and is thrust bythe vanes of the impeller into the main chamber 17. The impeller impartsto the particles of material to be separated a substantial velocity, forexample, within the range of about 1,000 to 1,200 feet per minute. Thisprevents the heavier particles from immediately dropping to the bottomof the chamber and causes the particles to pass across the chamber andbe subjected to the upward passing currents within the main separatingchamber 17. The lighter particle fraction is carried upwardly by theupwardly moving air currents as shown at 18, while the heavier particlefraction passes across the chamber as shown at 19, and may abut the wall20 of the chamber which is opposite the impeller 16. The heavierparticles may drop down onto a perforated plate 21 which is inclineddownwardly from the vane 22 of the air jet impeller assembly 22a or fallout of the air stream in the area near the wall 20 of the main chamber17. Because of the jet nozzle 22N formed by the air jet impellerassembly, the material coming off of the vane 22 is directed into a higharc trajectory as desired. This new air jet itself acts to break tanglesor dislodged particle. In addition, the jet propels the product into thehigh arc trajectory allowing more time for the separating air tointeract with it and finally, as the heavy material takes a moredownward course at the end of its trajectory, it falls into the area ofhighest velocity. Because the tobacco is moving downward against theupward air flow, the relative air velocity is increased without anincrease in the air flow further enhancing the separation.

By the present arrangement, the air flow is crowded towards the lower ordischarge end of plate 21, producing a higher degree of separation andallowing for makeup air to the heavies circuit with diminished downflowair currents. As this air flows upward, it expands toward the wallopposite the inlet and as it leaves the separating area slows to avelocity yielding good stem content.

The lighter particle fraction passes upwardly through the mainseparating chamber 17 with the air current passing upwardly through thechamber and through a substantially tangential passageway 23 into asubstantially cylindrically chamber 24. Centrally disposed within thechamber 24 is a cylindrical screen 25 which is mounted for rotationwithin the chamber. The screen 25 is of a mesh size insufficient topermit the passage of the lighter fraction particles which are carriedby the air currents, but permit the air to pass therethrough into thecentral portion 26 and thence outwardly through the open ends of therotary screen. The air passing through the rotary screen 25 and throughthe open ends of the screen passes into downwardly inclined ducts 27which merge inwardly to a housing 27A above and communicating withdamper section 27C having motorized dampers 27D. The damper section 27Coverlies a large plenum or settling chamber 28 flanked by a pair ofrotary fans 28F which draw air through the ducts 27, and force the airthrough the fan outlet 29 and back into the lower end portion of theseparating chamber 17. Thus it can be seen that there is a recirculatingsystem for the air used to effect the separation between the lighter andheavier particle fractions. This recirculating circuit comprises themain chamber 17, the passageway 23, through the rotary screen 24, andoutwardly through the open ends of the screen and downwardly throughducts 27, housing 27A, damper section 27C, plenum or settling chamber 28and fans 28F, and through the fan outlet 29 back through the lower endof the separating chamber 17. The lighter particles fraction passesdownwardly within the cylindrical chamber 24 and into an air lock 30.The lighter particle fraction then drops from the air lock 30 onto thetake-away belt 31 to be delivered through one side of the casing forcollection at a location spaced from the pneumatic separator.

The prior art pneumatic separator of the type disclosed in U.S. Pat. No.3,608,716 employed an endless foraminous belt, indicated by referencecharacter 11 in that patent, supported by and driven from end rolls.These heavier particles which rest on the foraminous belt were carriedalong the belt to the heavier particle fraction outlet, indicated byreference character 14 in that earlier patent, and by referencecharacter 35 in the drawings of the present application. The inlet forthe heavier particle fraction air conveying system was shown at 17 inthat patent and indicated at 36 in the drawings of the presentapplication and the conveying air in the device of the prior patent wasconveyed along the passageway, there indicated at 17, into a chamberwhere a portion of the air was drawn off and the main portion of the airpassed through the chamber and back through the passageway 20,corresponding to the passageway 34 of the present application, to theheavier particle fraction outlet 35. Also in the device of the earlierU.S. Pat. No. 3,608,716, a diffuser was provided, indicated by referencecharacter 36 in that patent, providing a series of angularly extendingspaced vanes which extend across the separating chamber, so that airpassing from the circulating fan outlet passed upwardly through thediffuser and through the lower and upper runs of the endless belt. Thediffuser 36 was designed to cause an even flow of air up through themain separating chamber with a uniform velocity across the chamber.

The present invention differs from the foraminous endless belt anddiffuser assembly of the earlier apparatus to effect a substantialimprovement in the separation of stem and good material. As previouslydescribed, a very high air velocity will separate more of the goodmaterial with the drawback of also carrying along stem, flag, andunthreshed leaves leading to an unacceptable high stem content. Use of ahigh velocity air stream to separate and then slow the air to drop stempermits one to obtain a high separating efficiency and a low stemcontent. Accordingly, in the apparatus of the present invention, an airdiffuser assembly, indicated generally by the reference character 37 isprovided, receiving a large portion of the air discharged through theoutlet 29 of the rotary fan in the fan casing 28, and directing this airupwardly toward the main chamber 17. The air diffusion grating of theearlier U.S. Pat. No. 3,608,716 is replaced with a plurality ofadjustable directional vanes 38 and fixed directional vanes 39 arrangedto reduce the air flow and velocity in some portions of the separatingsection while greatly increasing it in other portions. As will be seen,the vanes 38 are adjustably supported on the frame members 40 fixed inthe housing and located above the wall 41 defining the lower wall of theoutlet duct 29 from the fan in the fan housing 28, the vanes 38 beingsupported on shafts which extend through openings in the side members ofthe frame 40 and being adjustable by a threaded bolt system or otherknown means for fixing the ends of the shaft at various angularpositions.

The directional vanes 39 are fixed to the frame 40 and arranged in apattern to produce the desired variation in the air flow and velocity inthe different portions of the separating section. By this arrangement,the air flow can be selectively directed for maximum separatingefficiency and low stem content. The fixed perforated plate 21, arrangedin an inclined position as illustrated, replaces the diffusion belt ofthe earlier device of U.S. Pat. No. 3,608,716, and has the advantage ofreducing the diffusion of the belt while containing the heavy particleswhich may fall upon it. Air flow in the area adjacent to the wallopposite to the inlet rotor 16 is restricted, and the flow near theheavies discharge under the inlet is increased.

Since stems on occasion may project into the perforations of the fixedperforated plate 21 and some small material may be held against thebottom of the perforated plate, a cylindrical brush, indicated at 43 ispositioned at the underside of the plate and is driven by two aircylinders or pneumatic cylinder and piston units, one of which isindicated at 44, located on opposite sides of the brush, and coupled tothe shaft of the brush 43 by bearings permitting rotation of the brush.Sprockets, one of which is indicated in broken lines at 45 are fitted tothe brush shaft at the opposite ends thereof, and are, in turn, mountedin bearings in the brush carriers forming the journal bearings for thebrush shaft at the ends of the piston arms of the two air cylinders 44.A roller chain, indicated at 46, is lead around the sprockets 45 andfixed to the machine frame at each end of the chain beyond the brushtravel path. As the air cylinders 44 move the brush along the undersideof the perforated plate 21, the chains 46 cause both ends of the brush43 to move together without cocking arising from one end advancing aheadof the other. The chains also cause the brush to rotate as it moves,greatly increasing its cleaning ability.

Air from the fan 28f in the fan housing 28 and discharged through thefan outlet 29 is divided, some of this air being directed by anadjustable deflecting vane 48 mounted at the downstream inlet edge of achimney or vertical duct 49 relative to the airstream discharge from thefan outlet 29, to pass into a chamber 49 and outwardly through twoopenings 50 provided in the wall 20 to pass additional separating airinto the upper portion of the main separating chamber 17. The remainderof the discharge air from the fan passes into the duct portion 51 to thezone below the adjustable directional vanes 38 and fixed directionalvanes 39 to provide the supply air passing upwardly through the spacesbetween these vanes and through the perforated inclined plate 21. Theamount of air passing into this duct portion 51 is further regulated byan adjustable damper 52. The device of the earlier U.S. Pat. No.3,608,716 employed an adjustable vane 35 at the lower end of the wall inthat patent which corresponds to the wall 20 of the apparatus of thepresent invention, which in the earlier patent was provided to create adead airspace immediately adjacent to this wall. In the presentapparatus, an adjustable vane, indicated at 22, is provided, at alocation generally corresponding to that of the fixed vane of theearlier device, so that any material reaching the wall 20 will falldownward and slide off the vane, referred to commonly as "ski jump",which is adjusted to a position and, because it was simply a downwardlydeclined vane directed at a converging angle toward the upper surface ofthe foraminous belt, essentially caused air coming under the vane, shownat 35 in the earlier patent, to follow the top of the belt. In thepresent arrangement, the vane 22 of the air jet impeller assembly 22Aalso includes an upwardly concave trough or guide surface 22T spacedjust below the free end of the vane 22 and positioned and shaped so thatthe air jet impeller directs the air so as to tend to throw the materialin the discharge zone of the jet impeller upward in a trajectory so thatit falls into the high velocity air area of the separating chamber 17 sothat the heavier materials are subjected to high velocity air. Thisgreatly increases the efficiency of the device in achieving separationof heavies from desired material.

Since the former air jet impeller of the earlier device was a fixeddirectional air flow arrangement introduced under the vane, although itassisted the material to return across the chamber, it in fact propelledit towards the heavies pickup and provided little opportunity forreseparation. By the present arrangement, the series of adjustable andfixed directional vanes 38 and 39 provide both high velocity and lowvelocity separating air with the same air flow and produce aconsiderably more efficient desirable separation of the materialsdelivered to the main chamber 17. The jet nozzle impeller which isadjustable in direction, flow quantity and velocity, enhances theability of the normal separating air to separate more efficiently byallowing more time for separation and increasing the relative velocityof the separating without increasing the air flow. Also the fixedperforated inclined plate 21, replacing the perforated be-t of the priordevice, and the cleaning device for the plate, adds to the separatingefficiency by reducing the diffusion of the air supply.

In the present arrangement, since most of the separating air is directedtoward the lower end near the heavies discharge, the separating airvelocity is low to nil in a triangular section along the portion of thewall 20 immediately above the air jet impeller assembly 22A. Lightmaterials, therefore, which fall out of the higher velocity air streaminto this low velocity area are subjected to the high velocity airstream discharged from the jet into the high arc trajectory, separatingthem readily from the heavies and thus reducing the possibility of theirremaining entrapped with the heavies. The adjustable deflecting vane 48in the discharge of the main separating air fan, located at the inlet tothe chimney or upwardly extending duct section 49, forces air up thechimney and through the openings 50 in the wall 20 of the separatingchamber 17. Thus the velocity in what is normally a dead area isenchanced preventing light materials from falling while not causing anincrease in the separating air velocity until after the separatingselection is completed. The shape of the main separating chamber 17 isalso altered relative to that of the apparatus of the earlier patent,providing a smaller tighter area producing air movement such that, asthe air moves upwardly in the approximately lower half of the separatingchamber in the zone immediately in the discharge path from the rotaryimpeller 16, the chamber becomes larger, the air slows down, and moreefficient separation is achieved.

It will also be noted, that as part of the air circuit, the large plenumor settling chamber, indicated at 28, has been provided to allow thesand or silica which was initialiy stuck to or embedded with the tobaccoand separates therefrom to settle out of the airstream prior to enteringthe fans 28F. This feature makes it possible to use lighter constructionfor the fan wheels providing higher efficiency with considerable savingsto the user in power costs, and permits avoidance of the need for heavylow efficiency fans subjected to very high wear.

I claim:
 1. A pneumatic separator for separating lighter particles fromheavier stem particles and the like, as in tobacco threshing, comprisinga separating chamber, means for circulating air in a generally upwardpath through said chamber, inlet rotary impeller means mounted on oneside of said separating chamber having vanes for thrusting particles tobe separated into and across the chamber toward a generally upwardlyextending opposite wall of said chamber, an inclined perforated platemember defining a bottom wall portion of said chamber below the level ofsaid impeller means for directing larger particles discharged toward orfalling onto the inclined plate member for collecting and carryingheavier particles from the chamber, an air jet impeller means locatedimmediately above said inclined plate at a lowermost portion of saidopposite wall and means for conducing air to said jet impeller means todischarge an air jet therefrom for directing material into a high arctrajectory into said chamber, an air diffusion grating assembly belowsaid inclined perforated plate member receiving air discharged from afan and having a plurality of adjustable directional vanes and aplurality of fixed direction vanes, a first group of said vanes beingpositioned and oriented to reduce air flow and velocity in selectedportions of the separating chamber lying above said first group and asecond group of said vanes being positioned and oriented to increase airflow and velocity in other portions of the separating chamber lyingabove said second group to selectively direct upward air flow throughsaid chamber for maximum separating efficiency, and said upwardlyopening opposite wall having discharge openings located at a verticalposition above said level of said impeller means and means for supplyingair through said openings to provide air flow therethrough into saidchamber in zones located above the height of said openings.
 2. Apneumatic separator as defined in claim 1, wherein said air jet impellermeans includes an adjustable inclined pivoted vane separate from saidadjustable vanes pivoted at one end thereof immediately below saidlowermost portion of said opposite wall and a concave curved sheetmember spaced a predetermined distance from and confronting a free endof said inclined pivoted vane defining an air jet discharge nozzle withsaid pivoted vane coactive therewith for adjusting direction, flowquantity and velocity of the air jet discharged therefrom.
 3. Apneumatic separator as recited in claim 2, wherein said adjustable andfixed directional vanes in the air diffusion assembly provide both highvelocity and low velocity separating air with the same air flow sourcebeing discharged from said fan and direct the same upwardly through saidseparating chamber with the upwardly moving air being distributednonuniformly across the separating chamber in a predeterminedrelationship to achieve maximum separating efficiency.
 4. A pneumaticseparator as defined in claim 3, including cleaning apparatus forcleaning said inclined perforated plate member, the plate member havinga width to extend entirely across the chamber and having an uppermostend and a lowermost end, the cleaning apparatus comprising a rotatablebrush member having a brush surface bearing upwardly against anunderside of the inclined perforated plate and rotatable about an axisof rotation paralleling said inclined perforated plate and transverselyspanning the width thereof, and means for moving said brush in areciprocative rectilinear path paralleling said inclined perforatedplate from the uppermost end to the lowermost end thereof.
 5. Apneumatic separator as defined in claim 2, including cleaning apparatusfor cleaning said inclined perforated plate member, the plate memberhaving a width to extend entirely across the chamber and having anuppermost end and a lowermost end, the cleaning apparatus comprising arotatable brush member having a brush surface bearing upwardly againstan underside of the inclined perforated plate and rotatable about anaxis of rotation paralleling said inclined perforated plate andtransversely spanning the width thereof, and means for moving said brushin a reciprocative rectilinear path paralleling said inclined perforatedplate from the uppermost end to the lowermost end thereof.
 6. Apneumatic separator as recited in claim 1, wherein said adjustable andfixed directional vanes in the air diffusion grating assembly provideboth high velocity and low velocity separating air with the same airflow source being discharged from said fan and direct the same upwardlythrough said separating chamber with the upwardly moving air beingdistributed nonuniformly across the separating chamber in apredetermined relationship to achieve maximum separating efficiency. 7.A pneumatic separator as defined in claim 6, including cleaningapparatus for cleaning said inclined perforated plate member, the platemember having a width to extend entirely across the chamber and havingan uppermost end and a lowermost end, the cleaning apparatus comprisinga rotatable brush member having a brush surface bearing upwardly againstan underside of the inclined perforated plate and rotatable about anaxis of rotation paralleling said inclined perforated plate andtransversely spanning the width thereof, and means for moving said brushin a reciprocative rectilinear path paralleling said inclined perforatedplate from the uppermost end to the lowermost end thereof.
 8. Apneumatic separator as defined in claim 1, including cleaning apparatusfor cleaning said inclined perforated plate member, the plate memberhaving a width to extend entirely across the chamber and having anuppermost end and a lowermost end, the cleaning apparatus comprising arotatable brush member having a brush surface bearing upwardly againstan underside of the inclined perforated plate and rotatable about anaxis of rotation paralleling said inclined perforated plate andtransversely spanning the width thereof, and means for moving said brushin a reciprocative rectilinear path paralleling said inclined perforatedplate from the uppermost end to the lowermost end thereof.